1. Field of the Invention
The present invention relates generally to telephone line overvoltage protection devices, and more particularly to an improved telephone line overvoltage protection method and apparatus.
2. Description of the Prior Art
Overvoltage protection devices are commonly used with telephone lines for protecting telephone equipment against hazardous voltages due to lightning or power surges. Overvoltage protection circuitry that overcomes many disadvantages of the prior art circuitry is disclosed in McCartney, U.S. Pat. No. 4,758,920, issued Jul. 19, 1988; and McCartney et al., U.S. Pat. No. 4,941,063, issued Jul. 10, 1990; and both are assigned to the assignee of the present invention.
An inert, gas-filled, protective device or gas discharge tube with electrodes inserted between TIP and RING INPUT connections often is used for protection from hazardous voltages, for example, due to lightning and power surges. A significant disadvantage of the inert, gas-filled, protective device or gas discharge tube is the relatively long response time delay as compared to a solid-state device. However, known protective arrangements that utilize a solid-state device do not provide balanced operation in a failure mode to shunt both the TIP and RING to ground. A need exists for a first protective device having a short response time delay and providing effective failure mode balanced operation.
Other problems with known protection devices generally effective for overvoltage noise and transient protection include the complexity, the difficulty and time required for manufacture and assembly.